The present invention relates to a disc brake for an automotive vehicle, wherein the disc brake comprises a housing, a brake disc rotatable relative to the housing, at least one friction pad, and at least one actuation device, which is formed to effect a relative movement between the brake disc and the friction pad, such that the friction pad can be brought into contact with the brake disc, wherein the actuation device has at least one actuating piston movable along a piston longitudinal axis, which actuating piston is guided in a hydraulically sealing manner within the housing by means of a sealing arrangement having a sealing ring, wherein the actuating piston is movable within the housing both by means of applying hydraulic pressure of a hydraulic chamber formed in the housing and by means of a mechanical actuator, wherein the sealing ring is taken up in an annular groove formed in the housing.
Disc brakes of this kind are known from the prior art.
In the case of such disc brakes, the actuating piston can be moved both hydraulically as part of normal service braking and mechanically by means of an actuator arrangement to activate a parking brake function. In both instances of movement, the piston must be guided in a sealing manner within the housing to prevent an escape of hydraulic fluid from the hydraulic chamber. To do this, a sealing ring is normally provided in an annular groove formed in the housing, which ring guides the movably guided piston in a sealing manner. In this context it was recognised that conventional sealing arrangements, in which a sealing ring is simply inserted into a corresponding annular groove, can lead to significant difficulties in the interaction between instances of service braking and activations of the parking brake function carried out in the interim. This is due to the fact that disregarding measures to compensate for wear on the brake pads the piston stroke of the actuating piston that takes place during normal service braking only comprises relatively short distances, wherein in such service braking the sealing ring adheres to the external circumferential surface of the piston on account of the adhesive friction on this. In other words, during normal service braking the piston does not slip through the sealing ring. Instead, the sealing ring is deformed only elastically on account of the piston movement caused hydraulically. If the hydraulic pressure in the hydraulic chamber is released on termination of the braking, the actuating piston returns to its original state due to the substantially purely elastic deformation of the sealing ring during braking and the elastic relaxation following this, as described in the documents DE 30 24 299 A1, U.S. Pat. No. 4,156,532 and JP H11-280 805 A, for example. Residual abrading torques following service braking between the brake disc and the pressed-on brake pads can be effectively suppressed in this way. The reset movement of the elastically deformed sealing ring is supported in particular also by the hydraulic pressure present on the side of the sealing ring directed towards the hydraulic chamber. This hydraulic pressure has considerable influence on the elastic deformation behaviour of the sealing ring in service braking and on its relaxation and deformation recovery when the hydraulic pressure is released.
If the parking brake is now activated by means of the mechanical actuator, however, a movement of the actuating piston takes place, so to speak, but not due to application of the hydraulic pressure in the pressure chamber, but rather due to actuation of the mechanical actuator. In an activation of the parking brake in this way, the hydraulic deformation support falls away due to the lack of hydraulic pressure present in the hydraulic chamber, therefore, so that the deformation behaviour of the sealing ring also changes. Hydraulic pressure no longer acts upon the sealing ring on the hydraulic chamber side and it is accordingly not sufficiently strongly deformed and pressed against the external circumferential surface of the actuating piston to maintain the adhesive friction, as is the case in normal service braking. The risk accordingly arises when activating the parking brake via the actuator that when the actuating piston moves, it overcomes the adhesive friction between actuating piston and sealing ring and ultimately slips through the sealing ring by a certain distance. If the parking brake is later released again, the sealing ring no longer provides the elastic reset movement that is usually effective during service braking due to this slipping through. This means that the actuating piston largely remains in its position that it assumed during the activated state of the parking brake. As a consequence, residual abrading torques that are considerable in some cases and are accompanied by disadvantages such as pad wear, increased fuel consumption, noise emission etc. occur following the actual release of the parking brake.
To tackle this problem, the prior art according to WO 2007/12086 A1 proposes to provide the annular groove with a groove floor running obliquely, in which the depth of the groove increases continuously transversely to the piston longitudinal axis in the return stroke direction. A force component is thus to be attained in the reset direction that acts in a similar manner to a downhill-slope force and moves the sealing ring away from the flank of the groove on the closing side.
The document WO 2012/016612 A1 also tackles the problem described above arising from the interplay between service braking and activation of the parking brake. In this solution, however, the occurrence of residual abrading torques following the activation of the parking brake is counteracted not by configuration of the annular groove, but rather by targeted use of a slip control system.
Further prior art is known from the document DE 16 55 485 A.